docs: def check_vertical_extents(self, ds):
          """
          Check that the values of geospatial_vertical_min/geospatial_vertical_max approximately match the data.
  
          :param netCDF4.Dataset ds: An open netCDF dataset
          """
          if not (hasattr(ds, 'geospatial_vertical_min') and hasattr(ds, 'geospatial_vertical_max')):
              return
  
          z_variable = cfutil.get_z_variable(ds)
          if not z_variable:
              return Result(BaseCheck.MEDIUM,
                            False,
                            'geospatial_vertical_extents_match',
                            ['Could not find vertical variable to test extent of geospatial_vertical_min/geospatial_vertical_max, see CF-1.6 spec chapter 4.3'])
          if ds.variables[z_variable].dimensions == tuple():
              return self._check_scalar_vertical_extents(ds, z_variable)
  
          return self._check_total_z_extents(ds, z_variable)